1. Field of the Invention
The present invention relates to polymeric blends which are useful as non-halogen flame and oil-resistant materials.
2. Description of Related Art
Ethylene vinyl acetate copolymers and copolymeric blends are known. U.S. Pat. No. 4,338,227 describes various copolymers and uses thereof. Ethylene vinyl acetate copolymeric resins typically offer excellent crack resistance and maintain flexibility over a broad temperature range of -60.degree. C. to 150.degree. C. without the need for plasticizers. Ethylene vinyl acetate carbon monoxide is a known terpolymer--commonly used as a resin modifier for PVC. It is also referred to as a plasticizer. It is also known that while high vinyl acetate ethylene-vinyl acetate copolymers (EVA) formulated with hydrated fillers provide non-halogen flame, low smoke and oil-resistant properties to components (wire and cables) made from such polymeric material, the resin pellets tend to be sticky and agglomerate which provides disadvantages in production and handling. The present inventor has discovered, however, that increasing the vinyl acetate content and advantages associated therewith can be accomplished by formulating a blend as recited and claimed below which provides improved non-halogen flame and oil resistance to materials made from such a blend while concurrently eliminating the disadvantages associated with the high vinyl acetate ethylene copolymers while retaining satisfactory heat resistant properties. The blend of the invention is in a free-flowing undusted form which has lower viscosity for advantages in processing; the blend has improved low temperature capability (flexibility) and it surprisingly has improved or increased tensile strength.
Improved flexibility at low temperatures extends the range of operability for a material. Materials that loose flexibility and become brittle tend to crack and fail with movement.
Lower resin blend viscosity translates to lower wire extruder pressures and easier extrusion with potential for greater through put rates. Free-flowing pellets allow easier handling and use in continuous mixing equipment such as continuous mixers and buss co-kneaders. Convenient air-suction transport of material is possible also. Dusted pellets can result in problems of either too little or too much dusting agent. With too little surface dusting, pellets may agglogmerate and make difficult or impossible air-suction or gravity-flow handling. With too much surface dusting, the dusting agent can become concentrated creating inconsistent flow and other handling difficulties.
High tensile strength provides the mechanical properties needed to meet the requirements of the application and long-term serviceability. Mechanical property requirements vary with the end-use application but generally higher mechanical strength, such as tensile, is desirable for enhanced product durability. The present invention as a blend of known polymeric materials with additional excipients provides significant process advantages by enhancing the polarity of the blend without requiring high vinyl acetate percentages in an ethylene/vinyl acetate copolymer. The inventor has discovered that a blend using a compatible terpolymer having ethylene/vinyl acetate/carbon monoxide provides the necessary polarity presumably because of the relative polarity of the carbon monoxide.